1. Field of the Invention
The present invention relates to an Electron Emission Display (EED), and more particularly, to an EED which can reduce noise influence transferred through a ground between a high voltage element and a low voltage element.
2. Description of the Related Art
An Electron Emission Display (EED) includes an EED panel and a driver. When the driver supplies a positive voltage to an anode of the EED panel, if a positive voltage is supplied to a gate electrode and a negative voltage is supplied to a cathode electrode, electrons are emitted from the cathode. The emitted electrons are accelerated toward the gate electrode and converged into the anode. Then, the electrons collide with fluorescent cells disposed in front of the anode, thereby emitting light.
The driver includes a video processor to convert an external analog video signal into a digital signal, a panel controller to generate driving control signals according to the internal video signal, a data driver and a scan driver to process the driving control signals and to output the processed control signals to electrode lines of the EED panel. The electrode lines include cathode electrode lines and gate electrode lines, which receive RF high voltage from the data driver and the scan driver, and an anode connected to a high voltage power supply.
Voltages supplied to the cathode electrode lines, the gate electrode lines and the anode are very high compared with those supplied to logic circuits of the drivers. Therefore, when a high voltage element and a low voltage element make use of a common ground, RF noise generated by the high voltage element is transferred to the low voltage element through the ground, causing an error in the low voltage element, for example, a logic circuit.
Also, the cathode electrode lines, the gate electrode lines and the anode are supplied with different high voltages rather than equal high voltages. Thus, RF noise has a bad influence upon them mutually. Specifically, as a frequency of a high voltage pulse supplied to the drivers increases, RF noise increases as much. In a large-size panel, data signals and scan signals must be supplied to more pixels with respect to the same horizontal and vertical synchronization signals. Thus, the frequency inevitably becomes higher. As the panel becomes larger in size, it needs to be designed considering the noise.
Furthermore, when a digital logic element and an analog logic element operate at a high frequency, the low voltage elements (logic elements) can also be mutually influenced by RF noise. Thus, noise reduction is necessary between the digital logic element and the analog logic element.
In an EED, low voltage elements (logic elements) and high voltage elements are commonly grounded. One side of the EED includes a substrate on which high voltage elements and low voltage elements are mounted together, and another side includes a high voltage element.
The low voltage logic element includes digital logic elements and analog logic elements and usually operates with ±5 V. As to the high voltage elements, a high voltage of ±50-100 V is supplied to a gate electrode line or data electrode line of the EED panel. A high voltage of about 4000 V is supplied to an anode. As to the digital logic elements, the driver is supplied with a high voltage in order to control a high voltage, which is supplied to the data electrode lines and scan electrode lines of the panel.
Therefore, the logic circuits, such as the driver for controlling the high voltage, are low voltage elements on the one hand, but are high voltage elements on the other hand. Since the high voltage elements are driven at an RF high voltage, noise occurs therein. The noise influences the low voltage elements through the ground.
For example, noise occurring in the anode having an electrical potential of 4 kV can influence the digital logic element and the analog logic element through the ground. Also, RF noise occurring in the high voltage element can influence other digital logic elements through the ground. Thus, the EED has a problem in that the picture quality of the images displayed on the EED panel is degraded.